Pipes, pipe members, pipe spools, and other cylindrical objects such as tanks (hereinafter collectively referred to as pipe members) are traditionally joined by flanges. When two pipe members are joined by means of respective flanges, the flanges are in fact restrained joints that transfer axial loads between the pipe members. These axial loads are transferred between the pipe members via the flange hub, the flange, and the flange bolts. Because of the eccentricity of the flange bolts with respect to the pipe members' wall, this transfer of axial loads results in significant twisting loads on the flange and hub.
Various methods of connecting fibre-reinforced plastic pipes exist. The state of the art includes U.S. Pat. No. 4,619,470, which discloses how a pair of fibre-reinforced plastic pipe members are joined together in a flanged connection. The pipe members are formed to include an inner pipe jacket consisting essentially of a thermoplastic material and an outer pipe jacket consisting essentially of a fibre winding impregnated with a synthetic resin. A threaded section is formed in each of the outer pipe jackets at the end of each of the pipe members, a flange bushing is provided with a loose flange ring threadedly engaged on each of the threaded sections, and a covering collar covering at least the end of each of the pipe members is inserted at the inner pipe jacket.
The state of art the also includes U.S. Pat. No. 3,796,449, which describes a molded plastic flange encircling the exterior end portion of a fibre-reinforced plastic (FRP) pipe body. The flange has an elongated hub and a central bore extends through the flange and hub. The pipe body makes a tight fit in the bore, and a layer of adhesive (preferably epoxy resin with a filler of e.g. sand), bonds the inner diameter of the flange to the exterior of the pipe body. In one embodiment, the flange inner diameter is threaded onto the pipe body. A series of circumferentially spaced apart bolt holes are formed in flange, the bolt holes providing means for securing the flange to the flange of an adjoining pipe. A reinforcing ring, embedded in the hub, encircles pipe body. The flange is described as being made of fibre-reinforced plastic and the reinforcing ring is preferably made of a material having a higher Young's modulus than that of the plastic pipe body or the plastic flange. The reinforcing ring preferably is an integral steel O-ring, or can be made of multiple steel wires.
The state of the art also includes U.S. Pat. No. 4,813,457, disclosing a flange made of fibre-reinforced thermosetting synthetic resin. The flange comprises at least one flange section extending in an axial direction, which is fitted, or can be fitted, on a tubular part to be provided with a flange. The flange section joins the inside face of the flange which, together with an outside face of the flange, defines the flange. The flange has several fibre-reinforcement layers laid around each other and extending in an axial direction, and which are spirally wound up. The flange section extending in the axial direction also consists of fibre-reinforcement layers and thermosetting synthetic resin. In the region of the angular intersection between the inside face of the flange and the flange section extending in the axial direction, a reinforcement layer is arranged in order to prevent crack formation. The reinforcement layer extends from the inside face of the flange to the flange section extending in the axial direction. The reinforcement layer may be formed by a disc-shaped fibre-reinforcement layer having a central opening, or may consist of a layer of spun roving. The flange section is formed by spirally winding a glass fabric strip soaked in thermosetting synthetic resin. The glass fabric strip has a greater width than the width of the flange winding mould, as a result of which the strip is either provided with corrugations or bent over at its ends which lie up against the inside and outside faces of the flange.
While many of the known flange designs and methods of manufacture work well for smaller diameter flanges, they often tend to be costly for larger diameters. Practical constraints in reinforcement placement and orientation also often limit structural efficiency, especially for the larger flanges.
The applicant has devised and embodied the invention to overcome certain shortcomings of the prior art and to obtain further advantages.